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linux/fs/xfs/linux-2.6/xfs_vfs.h
David Chinner 92821e2ba4 [XFS] Lazy Superblock Counters 
When we have a couple of hundred transactions on the fly at once, they all
typically modify the on disk superblock in some way.
create/unclink/mkdir/rmdir modify inode counts, allocation/freeing modify
free block counts.

When these counts are modified in a transaction, they must eventually lock
the superblock buffer and apply the mods. The buffer then remains locked
until the transaction is committed into the incore log buffer. The result
of this is that with enough transactions on the fly the incore superblock
buffer becomes a bottleneck.

The result of contention on the incore superblock buffer is that
transaction rates fall - the more pressure that is put on the superblock
buffer, the slower things go.

The key to removing the contention is to not require the superblock fields
in question to be locked. We do that by not marking the superblock dirty
in the transaction. IOWs, we modify the incore superblock but do not
modify the cached superblock buffer. In short, we do not log superblock
modifications to critical fields in the superblock on every transaction.
In fact we only do it just before we write the superblock to disk every
sync period or just before unmount.

This creates an interesting problem - if we don't log or write out the
fields in every transaction, then how do the values get recovered after a
crash? the answer is simple - we keep enough duplicate, logged information
in other structures that we can reconstruct the correct count after log
recovery has been performed.

It is the AGF and AGI structures that contain the duplicate information;
after recovery, we walk every AGI and AGF and sum their individual
counters to get the correct value, and we do a transaction into the log to
correct them. An optimisation of this is that if we have a clean unmount
record, we know the value in the superblock is correct, so we can avoid
the summation walk under normal conditions and so mount/recovery times do
not change under normal operation.

One wrinkle that was discovered during development was that the blocks
used in the freespace btrees are never accounted for in the AGF counters.
This was once a valid optimisation to make; when the filesystem is full,
the free space btrees are empty and consume no space. Hence when it
matters, the "accounting" is correct. But that means the when we do the
AGF summations, we would not have a correct count and xfs_check would
complain. Hence a new counter was added to track the number of blocks used
by the free space btrees. This is an *on-disk format change*.

As a result of this, lazy superblock counters are a mkfs option and at the
moment on linux there is no way to convert an old filesystem. This is
possible - xfs_db can be used to twiddle the right bits and then
xfs_repair will do the format conversion for you. Similarly, you can
convert backwards as well. At some point we'll add functionality to
xfs_admin to do the bit twiddling easily....

SGI-PV: 964999
SGI-Modid: xfs-linux-melb:xfs-kern:28652a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>
2007-07-14 15:28:50 +10:00

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/*
* Copyright (c) 2000-2006 Silicon Graphics, Inc.
* All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef __XFS_VFS_H__
#define __XFS_VFS_H__
#include <linux/vfs.h>
#include "xfs_fs.h"
struct bhv_vfs;
struct bhv_vnode;
struct fid;
struct cred;
struct seq_file;
struct super_block;
struct xfs_mount_args;
typedef struct kstatfs bhv_statvfs_t;
typedef struct bhv_vfs_sync_work {
struct list_head w_list;
struct bhv_vfs *w_vfs;
void *w_data; /* syncer routine argument */
void (*w_syncer)(struct bhv_vfs *, void *);
} bhv_vfs_sync_work_t;
typedef struct bhv_vfs {
u_int vfs_flag; /* flags */
xfs_fsid_t vfs_fsid; /* file system ID */
xfs_fsid_t *vfs_altfsid; /* An ID fixed for life of FS */
bhv_head_t vfs_bh; /* head of vfs behavior chain */
struct super_block *vfs_super; /* generic superblock pointer */
struct task_struct *vfs_sync_task; /* generalised sync thread */
bhv_vfs_sync_work_t vfs_sync_work; /* work item for VFS_SYNC */
struct list_head vfs_sync_list; /* sync thread work item list */
spinlock_t vfs_sync_lock; /* work item list lock */
int vfs_sync_seq; /* sync thread generation no. */
wait_queue_head_t vfs_wait_single_sync_task;
} bhv_vfs_t;
#define bhvtovfs(bdp) ( (struct bhv_vfs *)BHV_VOBJ(bdp) )
#define bhvtovfsops(bdp) ( (struct bhv_vfsops *)BHV_OPS(bdp) )
#define VFS_BHVHEAD(vfs) ( &(vfs)->vfs_bh )
#define VFS_REMOVEBHV(vfs, bdp) ( bhv_remove(VFS_BHVHEAD(vfs), bdp) )
#define VFS_POSITION_BASE BHV_POSITION_BASE /* chain bottom */
#define VFS_POSITION_TOP BHV_POSITION_TOP /* chain top */
#define VFS_POSITION_INVALID BHV_POSITION_INVALID /* invalid pos. num */
typedef enum {
VFS_BHV_UNKNOWN, /* not specified */
VFS_BHV_XFS, /* xfs */
VFS_BHV_DM, /* data migration */
VFS_BHV_QM, /* quota manager */
VFS_BHV_IO, /* IO path */
VFS_BHV_END /* housekeeping end-of-range */
} bhv_vfs_type_t;
#define VFS_POSITION_XFS (BHV_POSITION_BASE)
#define VFS_POSITION_DM (VFS_POSITION_BASE+10)
#define VFS_POSITION_QM (VFS_POSITION_BASE+20)
#define VFS_POSITION_IO (VFS_POSITION_BASE+30)
#define VFS_RDONLY 0x0001 /* read-only vfs */
#define VFS_GRPID 0x0002 /* group-ID assigned from directory */
#define VFS_DMI 0x0004 /* filesystem has the DMI enabled */
/* ---- VFS_UMOUNT ---- 0x0008 -- unneeded, fixed via kthread APIs */
#define VFS_32BITINODES 0x0010 /* do not use inums above 32 bits */
#define VFS_END 0x0010 /* max flag */
#define SYNC_ATTR 0x0001 /* sync attributes */
#define SYNC_CLOSE 0x0002 /* close file system down */
#define SYNC_DELWRI 0x0004 /* look at delayed writes */
#define SYNC_WAIT 0x0008 /* wait for i/o to complete */
#define SYNC_BDFLUSH 0x0010 /* BDFLUSH is calling -- don't block */
#define SYNC_FSDATA 0x0020 /* flush fs data (e.g. superblocks) */
#define SYNC_REFCACHE 0x0040 /* prune some of the nfs ref cache */
#define SYNC_REMOUNT 0x0080 /* remount readonly, no dummy LRs */
#define SYNC_IOWAIT 0x0100 /* wait for all I/O to complete */
#define SYNC_SUPER 0x0200 /* flush superblock to disk */
#define SHUTDOWN_META_IO_ERROR 0x0001 /* write attempt to metadata failed */
#define SHUTDOWN_LOG_IO_ERROR 0x0002 /* write attempt to the log failed */
#define SHUTDOWN_FORCE_UMOUNT 0x0004 /* shutdown from a forced unmount */
#define SHUTDOWN_CORRUPT_INCORE 0x0008 /* corrupt in-memory data structures */
#define SHUTDOWN_REMOTE_REQ 0x0010 /* shutdown came from remote cell */
#define SHUTDOWN_DEVICE_REQ 0x0020 /* failed all paths to the device */
typedef int (*vfs_mount_t)(bhv_desc_t *,
struct xfs_mount_args *, struct cred *);
typedef int (*vfs_parseargs_t)(bhv_desc_t *, char *,
struct xfs_mount_args *, int);
typedef int (*vfs_showargs_t)(bhv_desc_t *, struct seq_file *);
typedef int (*vfs_unmount_t)(bhv_desc_t *, int, struct cred *);
typedef int (*vfs_mntupdate_t)(bhv_desc_t *, int *,
struct xfs_mount_args *);
typedef int (*vfs_root_t)(bhv_desc_t *, struct bhv_vnode **);
typedef int (*vfs_statvfs_t)(bhv_desc_t *, bhv_statvfs_t *,
struct bhv_vnode *);
typedef int (*vfs_sync_t)(bhv_desc_t *, int, struct cred *);
typedef int (*vfs_vget_t)(bhv_desc_t *, struct bhv_vnode **, struct fid *);
typedef int (*vfs_dmapiops_t)(bhv_desc_t *, caddr_t);
typedef int (*vfs_quotactl_t)(bhv_desc_t *, int, int, caddr_t);
typedef void (*vfs_init_vnode_t)(bhv_desc_t *,
struct bhv_vnode *, bhv_desc_t *, int);
typedef void (*vfs_force_shutdown_t)(bhv_desc_t *, int, char *, int);
typedef void (*vfs_freeze_t)(bhv_desc_t *);
typedef struct bhv_vfsops {
bhv_position_t vf_position; /* behavior chain position */
vfs_mount_t vfs_mount; /* mount file system */
vfs_parseargs_t vfs_parseargs; /* parse mount options */
vfs_showargs_t vfs_showargs; /* unparse mount options */
vfs_unmount_t vfs_unmount; /* unmount file system */
vfs_mntupdate_t vfs_mntupdate; /* update file system options */
vfs_root_t vfs_root; /* get root vnode */
vfs_statvfs_t vfs_statvfs; /* file system statistics */
vfs_sync_t vfs_sync; /* flush files */
vfs_vget_t vfs_vget; /* get vnode from fid */
vfs_dmapiops_t vfs_dmapiops; /* data migration */
vfs_quotactl_t vfs_quotactl; /* disk quota */
vfs_init_vnode_t vfs_init_vnode; /* initialize a new vnode */
vfs_force_shutdown_t vfs_force_shutdown; /* crash and burn */
vfs_freeze_t vfs_freeze; /* freeze fs for snapshot */
} bhv_vfsops_t;
/*
* Virtual filesystem operations, operating from head bhv.
*/
#define VFSHEAD(v) ((v)->vfs_bh.bh_first)
#define bhv_vfs_mount(v, ma,cr) vfs_mount(VFSHEAD(v), ma,cr)
#define bhv_vfs_parseargs(v, o,ma,f) vfs_parseargs(VFSHEAD(v), o,ma,f)
#define bhv_vfs_showargs(v, m) vfs_showargs(VFSHEAD(v), m)
#define bhv_vfs_unmount(v, f,cr) vfs_unmount(VFSHEAD(v), f,cr)
#define bhv_vfs_mntupdate(v, fl,args) vfs_mntupdate(VFSHEAD(v), fl,args)
#define bhv_vfs_root(v, vpp) vfs_root(VFSHEAD(v), vpp)
#define bhv_vfs_statvfs(v, sp,vp) vfs_statvfs(VFSHEAD(v), sp,vp)
#define bhv_vfs_sync(v, flag,cr) vfs_sync(VFSHEAD(v), flag,cr)
#define bhv_vfs_vget(v, vpp,fidp) vfs_vget(VFSHEAD(v), vpp,fidp)
#define bhv_vfs_dmapiops(v, p) vfs_dmapiops(VFSHEAD(v), p)
#define bhv_vfs_quotactl(v, c,id,p) vfs_quotactl(VFSHEAD(v), c,id,p)
#define bhv_vfs_init_vnode(v, vp,b,ul) vfs_init_vnode(VFSHEAD(v), vp,b,ul)
#define bhv_vfs_force_shutdown(v,u,f,l) vfs_force_shutdown(VFSHEAD(v), u,f,l)
#define bhv_vfs_freeze(v) vfs_freeze(VFSHEAD(v))
/*
* Virtual filesystem operations, operating from next bhv.
*/
#define bhv_next_vfs_mount(b, ma,cr) vfs_mount(b, ma,cr)
#define bhv_next_vfs_parseargs(b, o,ma,f) vfs_parseargs(b, o,ma,f)
#define bhv_next_vfs_showargs(b, m) vfs_showargs(b, m)
#define bhv_next_vfs_unmount(b, f,cr) vfs_unmount(b, f,cr)
#define bhv_next_vfs_mntupdate(b, fl,args) vfs_mntupdate(b, fl, args)
#define bhv_next_vfs_root(b, vpp) vfs_root(b, vpp)
#define bhv_next_vfs_statvfs(b, sp,vp) vfs_statvfs(b, sp,vp)
#define bhv_next_vfs_sync(b, flag,cr) vfs_sync(b, flag,cr)
#define bhv_next_vfs_vget(b, vpp,fidp) vfs_vget(b, vpp,fidp)
#define bhv_next_vfs_dmapiops(b, p) vfs_dmapiops(b, p)
#define bhv_next_vfs_quotactl(b, c,id,p) vfs_quotactl(b, c,id,p)
#define bhv_next_vfs_init_vnode(b, vp,b2,ul) vfs_init_vnode(b, vp,b2,ul)
#define bhv_next_force_shutdown(b, fl,f,l) vfs_force_shutdown(b, fl,f,l)
#define bhv_next_vfs_freeze(b) vfs_freeze(b)
extern int vfs_mount(bhv_desc_t *, struct xfs_mount_args *, struct cred *);
extern int vfs_parseargs(bhv_desc_t *, char *, struct xfs_mount_args *, int);
extern int vfs_showargs(bhv_desc_t *, struct seq_file *);
extern int vfs_unmount(bhv_desc_t *, int, struct cred *);
extern int vfs_mntupdate(bhv_desc_t *, int *, struct xfs_mount_args *);
extern int vfs_root(bhv_desc_t *, struct bhv_vnode **);
extern int vfs_statvfs(bhv_desc_t *, bhv_statvfs_t *, struct bhv_vnode *);
extern int vfs_sync(bhv_desc_t *, int, struct cred *);
extern int vfs_vget(bhv_desc_t *, struct bhv_vnode **, struct fid *);
extern int vfs_dmapiops(bhv_desc_t *, caddr_t);
extern int vfs_quotactl(bhv_desc_t *, int, int, caddr_t);
extern void vfs_init_vnode(bhv_desc_t *, struct bhv_vnode *, bhv_desc_t *, int);
extern void vfs_force_shutdown(bhv_desc_t *, int, char *, int);
extern void vfs_freeze(bhv_desc_t *);
#define vfs_test_for_freeze(vfs) ((vfs)->vfs_super->s_frozen)
#define vfs_wait_for_freeze(vfs,l) vfs_check_frozen((vfs)->vfs_super, (l))
typedef struct bhv_module_vfsops {
struct bhv_vfsops bhv_common;
void * bhv_custom;
} bhv_module_vfsops_t;
#define vfs_bhv_lookup(v, id) (bhv_lookup_range(&(v)->vfs_bh, (id), (id)))
#define vfs_bhv_custom(b) (((bhv_module_vfsops_t*)BHV_OPS(b))->bhv_custom)
#define vfs_bhv_set_custom(b,o) ((b)->bhv_custom = (void *)(o))
#define vfs_bhv_clr_custom(b) ((b)->bhv_custom = NULL)
extern bhv_vfs_t *vfs_allocate(struct super_block *);
extern bhv_vfs_t *vfs_from_sb(struct super_block *);
extern void vfs_deallocate(bhv_vfs_t *);
extern void vfs_insertbhv(bhv_vfs_t *, bhv_desc_t *, bhv_vfsops_t *, void *);
extern void vfs_insertops(bhv_vfs_t *, bhv_module_vfsops_t *);
extern void bhv_insert_all_vfsops(struct bhv_vfs *);
extern void bhv_remove_all_vfsops(struct bhv_vfs *, int);
extern void bhv_remove_vfsops(struct bhv_vfs *, int);
#endif /* __XFS_VFS_H__ */
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